One of the most important issue in these debates is defining "evidence". Evidence is an extremely subjective word because everybody has different standards of evidence that they will accept. Many times, the loftiness of those standards will correlate to the level of prejudice the individual already possesses against the idea he disbelieves. In other words, the higher the prejudice, the higher the standard of evidence they will require.
I once talked to an atheist that said the only form of evidence he would accept is - God appearing before him saying - "Hey, I'm God and I'm real", and then blinding him for 3 days so he would have physical evidence that he didn't hallucinate. That was the only standard of evidence that atheist would accept. Other atheists may have a more reasonable standard of evidence; but it's important for the theist to ascertain what that standard is, otherwise the theist ends up spending a lot of time spinning his wheels by providing all kinds of evidence that wouldn't be acceptable to the atheist in the first place.
I usually ask the atheist what he thinks acceptable/sufficient "evidence" for God would be in the first place. Since the atheist makes the positive affirmation that no such evidence exists, they obviously have an idea of what they think the evidence would be....or else they wouldn't be so certain they haven't already seen it.
Thus, its actually the atheist's responsibility to define what HE would personally accept as "sufficient" evidence for a god, and from there, the theist is required to analyze that standard of evidence to see if:
a) it is a reasonable and/or logically necessary standard
b) can be provided
I find that this approach saves A LOT of time because it cuts straight to the heart of the matter and eliminates all the rhetoric on both sides.